The overrunning of the U.S. consulate in Benghazi and the murder of the American ambassador to Libya are disastrous for U.S. intelligence-gathering capabilities in the Middle East. The resultant siege mentality in Washington creates an imperative to pull American spies and diplomats back into fortresses, heavily defended U.S. sanctuaries from which it’s almost impossible to collect good human intelligence.

Ambassador Christopher Stevens lost his life on Sept. 11 while doing his job representing the President. But never forget that ambassadors are also intelligence collectors. By wading in among the Libyans, from going to dinners at the homes of Libyan leaders to talking with ordinary people in the streets, he was gathering both important opinions and intelligence minutiae. It’s that daily immersion into the dynamics of a society that has always made the U.S. ambassador’s personal take on a situation as important as the judgment of any intelligence agency.

After Benghazi, however, we can all but assume that the White House and State Department will have near zero tolerance for exposing U.S. officials to the risks attached to mingling in the Middle East. In countries even lightly touched with the downsides of the Arab Spring, American diplomats and spies will be confined to heavily guarded facilities and allowed out only in highly conspicuous entourages of visibly armed guards, traveling in heavily armored vehicles.

None of this is new, of course. American diplomats and spies are already confined to bases in Iraq and Afghanistan, where they meet locals only when accompanied by small armies of security personnel — or when those locals are willing to enter U.S. facilities, passing through metal detectors and armed guards.

People unfamiliar with espionage may wonder, given the risk, what the downside is of making locals go to Americans. The problem is a basic one: any local with dangerous information worth having won’t risk passing through a security cordon. Even if the would-be informant were willing to risk being seen by hostile lookouts while approaching a U.S. facility, that person simply could not be sure that the American guards aren’t working for the enemy.

The damage caused by Benghazi isn’t limited to making it harder for the local mole or informant to hand over a packet of documents or a nugget of information to his American handler. Any good spy has to immerse himself in the local milieu — just as a great diplomat like Ambassador Stevens was doing. Night and day, the capable spy is out meeting with locals, having schooled himself in their language and customs. As soon as he gets off the plane at his new destination, he’ll start learning his way around the streets. It means endless driving, getting lost and finding your way back. And it’s always done alone, with no safe way to reach out to a local for help.

Maintaining direct contact with locals is the lifeblood of a spy seeking to understand a country. Most of what local sources say is of little or no interest to Washington, but such contact helps orient American intelligence officers and shows them how to find their way to real secrets. After Benghazi, that will be almost impossible to do. And keep in mind, sending out intelligence collectors disguised as students and businesspeople is just as risky and no more palatable to Washington.

The incidents of the past two weeks suggest it may be time to admit that large parts of the Middle East have fallen off the cliff for the U.S., and large parts of it will be beyond the ken of intelligence for the foreseeable future. Something terrible is going on in Syria, but because it’s too risky to put American intelligence officers on the ground there, it’s unclear just how terrible it is and how it could be ended. There’s simply no way for Americans to tell whether the armed rebellion is dominated by militant Islamists or Jeffersonian democrats. Nor can Americans get a picture of how the men leading the fighting forces on which Bashar Assad is most reliant might be turned.

This problem isn’t unique to Syria. A number of countries in the Middle East, from Lebanon to Yemen and from Jordan to Egypt, appear poised to fall into the political abyss. Consider Egypt: since the Muslim Brotherhood came to power, my sources tell me the army there is being purged of officers considered pro-American. I’ve been told that up to 4,000 officers have been let go, although I have no way to confirm that claim. But it would be surprising if the Muslim Brotherhood were not trying to cut Americans off from their traditional influence over the Egyptian military, just as the tragedy in Benghazi will likely cut off Americans’ access to ordinary Libyans.

Ambassador Stevens died a hero. Whether or not he took an unnecessary risk, he knew he couldn’t do his job while isolating himself from Libyans. The same holds true for American spies.

If the contagion in the Middle East continues to spread, the one thing Americans can count on is going blind — and it won’t be the fault of U.S. intelligence or anyone in Washington but just another sign of Americans’ declining position in the region.